Receiver for modulated radiofrequency pulses



May 8, 1951 H. RINIA RECEIVER FOR MODULATED RADIO FREQUENCY PULSES Filed Dec. 6, 1947 INVENTOR. 115E125 RZMA AGENZ Patented May 8, 1951 RECEIVER FOR MODULATED RADIO- FREQUENCY PULSES Herre Rinia, Eindlioven, Netherlands Application December 6, 1947, Serial No. 790,095

In the Netherlands November 30, 1942 2 Claims. (01. 25020) This invention relates to a device for the reception of signals characterized by impulses of constant duration and variable spacing.

In order to improve the signal-to-noise ratio in such systems it is known to make the incoming pulses. trigger an impulse repeater, i. e., a local impulse-generator.

According to the invention the signal-tc-noise ratio is materially improved with respect to the conventional devices by making use of an impulse repeater which, due to its response characteristic, exhibits an appreciable sensitivity decrease below the maximum value for a time corresponding at least to one cycle of the average impulse-repeating frequency of the incoming impulses.

Immediately after the occurrence of a repeated impulse, the impulse repeaters used in conventional devices regain their normal maximum sensitivity so that, for instance, a noise-impulse appearing midway between two successive signal impulses may bring about a repeated impulse.

In a circuit arrangement according to the invention, any response to such a noise-impulse is in general avoided, thereby improving the noiselevel.

Since the impulse repeater, notwithstanding its reduced sensitivity, might respond to noise impulses of excessive amplitude, it is advantageous to limit the amplitude of the impulses applied to the impulse-repeater.

The invention will now be described more fully with reference to the accompanying drawing forming a part of the specification and showing a schematic diagram of a circuit arrangement according to the invention.

In the form of construction represented the carrier-wave impulses picked up by an antenna are supplied to a high-frequency amplifier 2 which is connected in cascade with a mixer stage 3, an intermediate-frequency amplifier 4 and a detector 5. The pulse voltage obtained after detection is fed, preferably through a limiter 6, to a pulse repeater, that is a local impulsegenerator I which is known per se.

The local impulse-generator I consists of a multivibrator circuit arrangement comprising two discharge tubes Ill and II, the anodes of which are connected acros resistors 13 and [4 to a source of anode potential (not shown). The grids 25 and 26 of discharge tubes II and I are grounded through grid leak resistors l9 and 2!) respectively and coupled bymeans of capacitors l6 and I! to the anodes ,21and respectively.

. The repeated pulses taken from the cathoderesistor H are fed to a device 23 by which these pulses are converted into the signal to be utilized. Subsequently, the signal to be utilized is applied to a reproducing device 24.

The local impulse-generator has two positions of equilibrium. In one of these positions of equilibrium tube H is conducting and tube It is cut on, whereas in the other position of equilibrium tube 19 is conducting and tube H is cut off. The time during which the tubes are cut off is mainly-determined by the time constant of the capacitor [6 and resistor I 9, and the capacitor Hi and resistor 20 respectively.

In this circuit arrangement the time constant of resistor 29 and capacitor I? is such that whenever tube H is cut off, it will remain cut off at least for a time corresponding to the average impulse repeating frequency, whereas the time constant of capacitor l6 and resistor I9 is comparatively small and determines the duration of the repeated impulse.

Transition from one position of equilibrium to the other is eiiected by applying a pulse voltage of positive polarity and of such value to the grid of the non-conducting discharge tube Ill that the ignition voltage of this tube is attained.

Assume, in eiTect, that tube 10 is cut oii at a given instant. In this position of equilibrium the negative grid bias of tube I!) will decrease from the instant of cut off according to a discharge curve which is determined by the values of capacity of capacitor i7 and resistance of resistor 2B, the time constant being chosen in a manner such that this tube is cut off at least for a time corresponding to one cycle of the average impulse repeating frequency. Consequently, ignition of tube ill requires a voltage exceeding the momentary difference between ignition voltage and grid voltage, which means that noise impulses having a momentary amplitude smaller than said difference have no influence whatsoever. Due to this reduced sensitivity of the local impulse-generator the signalto-noise ratio is materially improved.

At the presence of a signal impulse on the grid of tube I0, the local impulse-generator will not have reached its maximum sensitivity, but the ignition voltage of the local impulse-generator is exceeded, as a result of which tube It] tends to draw current. The time during which tube I0 draws current is determined by the time constant of capacitor 16 and resistor IS. A renewed impulse is consequently taken from the cathode resistor 2%, the duration of which impulse corre 1. Apparatus for receiving a transmitted wave modulated by successive pulses the duration of which is constant and the spacing of which varies in accordance with an intelligence signal, said apparatus comprising a detector to demodulate said wave to derive said pulses therefrom, and a pulse-responsive generator coupled to said detector to repeat said derived pulses, said generator being constituted by a multivibrator system comprising first and second electron discharge tubes having a cathode a grid and an anode, means to cross couple saidtubes including a first capacitor connected between the anode of the first tube and the grid of the, second tub e and a second capacitor connected between the anode of the second tube and the grid of the first tube, a bias resistance connected between the grid of the first tube and ground to maintain said first tube normally non-conductive, the cathode of said second tube being grounded whereby said second tube is normally conductive, a first resistor connected between the grid of the firsttube and ground, a second resistor connected between the grid of the second tube and ground, means to apply said derived pulses to the grid of said first tube to render said tube conductive whereby said second tube is rendered non-conductive to develop a repeat pulse, said second capacitor in combination with said first resistor having a time constant at which subsequent to the occurrence of a repeat pulse said first tube is maintained 4 insensitive to voltages below the amplitude of said derived pulse for a period corresponding to the duration of one cycle of the average repetition frequency of said derived pulses, and a limiter interposed between said detector and said generator.

2. Apparatus, as set forth in claim 1, further includingrmeans coupled to theoutput of said generator to convert the repeated pulses issuing therefrom into a signal whose amplitude varies in accordance with the spacing of said repeated pulses.

HERRE RINIA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,262,838 Deloraine et a1 Nov. 18, 1941 2,338,395 Bartelink Jan. 4, 1944 2,361,437 Trevor Oct. 31, 1944 2,416,308 Gr eig Feb. 25, 1947 2,419,569 Labin Apr. 29, 1947 2,419,570 Labin Apr. 29, 1947 2,430,725 Miller et a1 Nov. 11, 1947 2,431,832 Schlesinger Dec. 2, 1947 2,468,059 Grieg Apr. 26, 1949 FOREIGN PATENTS Number Country Date 509,820 Great Britain July 19, 1939 

